Side Button Left Click?

Ok, so my mouse has side buttons that I can set specific functions to like macros (R-R-R as an example) or volume up/down. I was wondering if I could set one of the side buttons as a left click that would repeatedly left click as long as I was pressing down on the side button (I would change how fast it would left click based on attack speed of weapon). I would be moving around and actually playing the game and not afk-farming. Would this be allowed?

 

(B/c I can't understand english that well :P), so if the repeating left click only happens when I hold down the side button, would that be fine?

 

Alright thank you for the info!